The present invention relates to an excimer laser apparatus that uses r-are gases and hydrogen chloride gas as laser media for the emission of ultraviolet light. The apparatus includes a hydrogen chloride generator for supplying hydrogen chloride at a level appropriate for safe and efficient operation of the laser.
Excimer lasers are gas lasers which emit ultraviolet light in the range of 200-300 nm. In general, rare gas atoms, including argon (Ar), krypton (Kr), and xenon (Xe), are combined in their excited state with halogen atoms of fluorine (F), and chlorine (Cl) etc. to form a laser activator-excimer. When xenon (Xe) and chlorine (Cl) are combined, the resulting excimer laser has high emission efficiency, and therefore, is one of the most practical excimer lasers.
One of the greatest problems with a laser of this type is that the laser gas has a high reactivity and it reacts with the construction materials of the laser apparatus to degrade the quality of the laser gas. Generally, hydrogen chloride is used as a chlorine donor in the XeCl excimer laser. Chlorine (Cl.sub.2) is not used because it absorbs light of the laser emission wavelength of 380 nm.
The HCl and Cl atoms or Cl radicals generated during the production of the laser emission react with metallic materials to generate metal chlorides such as aluminum chloride (AlCl.sub.3) and ferric chloride (FeCl.sub.3), or react with plastic materials and O rings to generate carbon tetrachloride (CCl.sub.4) The laser light produced is also absorbed by these vaporized impurities. Further, the impurities will foul the laser window. Therefore, the impurities reduce the gas life of the XeCl excimer laser to the range of 10.sup.7 shots. Since a range of the 10.sup.9 shots is required for continuous operation in practical applications, the problem of the laser gas degradation must be solved for the excimer laser to become useful in industrial applications.
One solution to the problem of laser gas degradation is to cold trap the impurities, and then add a suitable amount of HCl. The impurities can be cold trapped because their vapor pressure is generally lower than that of Xe and HCl, and this purification method can extend the life of the laser gas.
The problem, however, with this method is determining the amount of HCl trapped and thus the amount of HCl to be added to maintain a concentration suitable for emission. Existing HCl testers are not dependable enough to be used for this purpose. In addition, the automatic supply of HCl from a gas supply bomb is dangerous because of its high toxicity, and there are other problems such as storing the HCl in the bomb, and the large ventilation equipment required.
Accordingly, this invention aims at solving the deficiencies of the XeCl excimer laser resulting from the supply of HCl. An object of this invention is to provide an excimer laser apparatus which has a safe, simple supply means of HCl so that the concentration of HCl may be automatically maintained at an appropriate level for a laser emission.